Amine-containing polymers are highly useful materials and represent a very cost effective way of incorporating cationic charge into polymers for uses such as cationic electrocoating, water treatment and enhanced oil recovery. Primary and, to a lesser extent, secondary amines offer the highest general reactivity spectrum of any group compatible with water. They will react with anhydrides, epoxides, isocyanates, esters, aziridines, aldehydes, ketones, Michael acceptors, aminoplasts and other alkylating agents to form covalent linkages. They react with acids and metal ions to form ionic linkages. Simple derivatives, e.g., Schiff bases, strongly and selectively complex many metal ions. This high reactivity enables many uses in areas such as coatings, adhesives, binders, structural polymers, viscosity control agents, ion exchange resins, and polymer boundary agents for bio-medical applications.
Because of their high electron donating ability when unprotonated and cationic charge when protonated, amine functional polymers offer superior adhesion to many types of substrates compared to other polymers which are typically neutral or anionic. The ability to change the reactivity and properties of primary or secondary amines by a simple pH change (addition of acid or base) offers numerous valuable options for viscosity control, emulsion stability control, polymer solubility modification (especially in water), or for formulating shelf-stable but reactive crosslinking or substrate reactive systems.
Synthesis of amine functional addition polymers in general is difficult for two reasons. The simplest amine functional monomer, vinyl amine, is thermodynamically and kinetically unstable relative to the isomeric Schiff base and condensation products of the base, ethylidene imine. Also, more stable allyl- and diallyl/amine monomers are expensive and typically show severe chain transfer during radical polymerization, especially involving allyl protons on carbon atoms alpha to the nitrogen. The allylamines are known to produce mainly low molecular weight polymers and copolymers, even using large amounts of free radical initiators.
For many purposes it is desirable to prepare water soluble polymers which contain relatively low levels of amine functionality, either to reduce costs by diluting the expensive amine component or for applications in which a lower level of cationic or reactive amine gives superior performance. A particularly attractive polymer for certain applications would be a vinyl alcohol copolymer with a low but controllable level of amine functionality.
Preparation of amine functional polyvinyl alcohol (PVOH) has been previously attempted by hydrolyzing copolymers of vinyl acetate and either N-vinyl-O-t-butyl carbamate or N-vinylacetamide. The carbamate monomer is prepared by a long and costly synthesis and is reported to hydrolyze to a highly toxic aziridine in the presence of water. In both cases the poly(vinyl acetate) component was hydrolyzed with methanolic or aqueous base. In the carbamate case, treatment of an aqueous solution of the poly(vinyl alcohol)-co-poly(N-vinyl-O-t-butyl carbamate) with acid gave the poly(vinyl alcohol)-co-poly(vinylamine) acid salt. Hydrolysis of the poly(N-vinylacetamide) is known to require strong acid at high temperatures. Both approaches produce a relatively dilute aqueous solution of the polymer which is expensive to store or ship or requires expensive additional steps to isolate the polymer from the solution. The aqueous solution also contains substantial amounts of frequently undesirable salts or acid.
It has been known for over 30 years that copolymers of vinyl alcohol containing a small amount of allylamine functionality could be prepared by copolymerization followed by hydrolysis. In U.S. Pat. No. 2,748,103, Priest (1956), reference is made to a hypothetical copolymer of vinyl alcohol and allylamine. This reference describes a method of making such copolymers containing 0.1 to 5.0% by weight of allylamines with the balance of the polymer being vinyl alcohol. The preparation is accomplished by copolymerizing a vinyl ester, for example vinyl acetate, and N-allylurethane followed by hydrolysis in two steps, first to convert the acetate groups to hydroxide groups, and secondly to convert the urethane groups to amine groups. The second step is carried out using 1 to 3% aqueous sodium hydroxide in the solution at 40.degree.-100.degree. C.
U.S. Pat. No. 3,032,539, Schuller, et al., (1962) discloses copolymerizating diallylamines and copolymerizable monomers containing ethylenic unsaturation such as styrene, vinyl acetate, acrylonitrile, acrylamide, methyl acrylates, and the like. The reference suggests 0.1 to 40 mole % diallylamine and 60 to 99.9% comonomer. It is stated that the procedure used yields linear polymers instead of a crosslinked polymer but the reason for this is not fully understood. There is no disclosure of converting such polymers by hydrolysis to copolymers of vinyl alcohol.
U.S. Pat. No. 4,393,174, Dawson, et al., (1983) discloses the base hydrolysis of polymers having pendant amide units, for example, N-vinylacetamide. The amide functionalities are converted with the polymers in solution to amine functionality using a strong aqueous base at elevated temperature.
U.S. Pat. No. 4,421,602, Brunnmueller, et al, (1983) describes polymerizing N-vinylformamide and hydrolysis of the formamide group in the presence of acid or base at 20.degree. to 200.degree. C. to form a polymer having 10 to 90% pendent amino groups and 90 to 10% pendent formyl groups. It is stated that such polymers are useful in paper making.
U.S. Pat. No. 4,490,557, Dawson, et al., (1984) discloses preparing ethylidene bisformamide, which is then pyrolyzed to N-vinylformamide which is then polymerized and the polymer is acid hydrolyzed to poly(vinylamines).
W. M. Brouwer, et al.; J. Polym. Sci. Polym. Chem. Ed., Vol. 22, pp. 2253-2362 (1984) describes the previously mentioned hydrolysis of a copolymer of poly(N-vinyl-O-t-butyl carbamate-co-vinyl acetate) to poly(vinylamines-co-vinyl alcohol). The author points out that the vinyl carbamate produces on aqueous hydrolysis a toxic product of ethylenimine.
R. W. Stackman, et. al.; Ind. Eng. Chem. Prod. Res. Dev., 24, 242-246 (1985) describes copolymerization of N-vinylacetamide (NVA) with vinyl acetate (VAc) as well as homopolymerization of the N-vinylacetamide. Hydrolysis of the acetamide polymer produces poly(vinylamine). It is stated that hydrolysis of the copolymer involves only the acetate groups initially, and hydrolysis of 20:80 NVA:VAc copolymer with base proceeded to 70% completion. Hydrolyzed copolymers are said to have formed clear films that were tougher than the homopolymer of N-vinylacetamide or the unhydrolyzed copolymer.
U.S. Pat. No. 4,713,236, Hoover, et al., (1987) describes preparation of a hair conditioning product containing a polymer with pendent amine or amine salt groups. This polymer can be prepared by hydrolysis of poly(N-vinylformamide) or poly(N-vinylacetamide). A copolymer of N-vinylacetamide with vinyl acetate can be formed which on hydrolysis produces a copolymer containing pendent hydroxyl and amino groups. Partial hydrolysis is said to be a way of modifying the polymer.
U.S. Pat. No. 4,772,359, Linhart, et al., (1988) describes a paper making process using as drainage aids and flocculants high molecular weight polymers of N-vinylamides, for example N-vinylformamide, including copolymers such as N-vinylformamide with vinyl acetate. These polymers are, however, not hydrolyzed.
U.S. Pat. No. 4,774,285, Pfohl, et al., (1988) describes copolymerization of N-vinylformamide (95-10%) and ethylenically unsaturated monomer (5-90 mole %), such as vinyl acetate or vinyl propionate and hydrolyzing 30 to 100% of the monomer units using hydrochloric acid or sodium hydroxide solution at 20.degree. to 100.degree. C. When NaOH solution is used at 50.degree. C., both the N-vinylformamide and the vinyl acetate groups are hydrolyzed to about equal extent. The polymers are useful in paper making.